Separation of aromatic hydrocarbons from non-aromatic hydrocarbons utilizing a lactam-water solvent



Aprll 19, 1960 R. D. MORIN ET AL 2,933,448

SEPARATION OF AROMATIC HYDROCARBONS FROM NON-AROMATIC HYDROCARBONS UTILIZING A LACTAM-WATER SOLVENT Filed Dec. 6, 1954 Solvent Raffinate l t TIO ll Storage Storage l l A 8 l l Water Extraction Column 3 5 7 g Extraction Column 2' \r i It l4 H =L. ll I9 '8 Condenser i 5 9 I l Extraction Aromatic I 3 Column Hydrocarbon Storage 1 Distillation |7 JON" INVENTOR. Richard D. Morin BY John B. Fishl n Arthur E. Bearse ATTORNEYS.

SEPARATION OF AROMATIC HYDROCARBONS FROM NON-AROMATIC HYDROCARBONS UTI- LIZING A LACTAM-WATER SOLVENT Richard D. Morin, John B. Fishel, and Arthur E. Bearse, 7

Columbus, Ohio, assignors, by mesne assignments, to The Ohio Oil Company, Littleton, Colo., a corporation of Ohio Application December 6, 1954, Serial No. 473,378

8 Claims. (Cl. 208-324) This invention relates to the separationof hydrocarbon mixtures. In particular, this invention is concerned with the separation of aromatic hydrocarbons from nonaromatic hydrocarbons. By aromatic hydrocarbons are meant those hydrocarbons which contain one or more benzene rings or related condensed aromatic rings such as naphthalene, phenanthrene, anthracene, acenaphthene, etc., and ,alkylated aand alkenylated derivatives of these. Nonaromatic hydrocarbons include the acyclic and alicyclic, saturated and unsaturated hydrocarbons.

Separation of these two classes of hydrocarbons has become of increasing importance industrially, and many methods have been proposed for the separation of aromatic from nonaromatic hydrocarbons. The complex mixtures of hydrocarbons which occur naturally in petroleum or those obtained from various refinery processing steps often contain mixtures of aromatic and nonaromatic hydrocarbons which are difiiculty separable from each other, if at all, by fractional distillation methods. Selective solvent extraction, selective adsorption on solid adsorbents such as silica gel, and extractive distillation have been used with varying degrees of success. In the selective solvent method, a solvent must preferentially dissolve the aromatic hydrocarbons to form a separable extract phase richer in aromatic hydrocarbons and a rafiinate poorer in aromatic hydrocarbons than the original hydrocarbon mixture. A good selective solvent should show a high degree of selectivity for aromatic hydrocarbons,should have a low solubility in the raftinate, should be readily separable from the aromatic hydrocarbons in the extract phase, should be easily recoverable, and should be stable to allow recycling. Solvents which have been used for selective extraction of aromatic hydrocarbons from mixtures with other hydrocarbons include sulfur dioxide,'furfural, diethylene glycol, polylethylene glycols, dimethyl formamide, oxydipropionitrile, thiodipropionitrile, etc. These solvents are not entirely suitable in all respects because of either one or more disadvantages due to poor selectivity, high solubility in the rafiinate, difiiculties in recovery, or instability in subsequent recycling.

The object of this invention is the separation of aromatic hydrocarbons from 'nonaromatic hydrocarbons by means of a selective solvent. A further object is to provide a method for obtaining aromatic hydrocarbons sub- 2 butenoic acid. These gamma-lactams may be represented by the structural formula I o R: wherein the gamma-butyrolactam skeletal nucleus may be either saturated or unsaturated and wherein R is either hydrogen or short-chain alkyl groups and R is a short chain alkyl group. It is to be understood that R may represent more than one short-chain alkyl group at tached to a substitutable carbon atom in the gammabutyr olactamskeletal nucleus. The substitution of alkyl groups in the gamma-butyrolactam nucleus decreases the selective efliciency of the compound, that is, selective efficiency of the solvents of this invention decreases as the length of the carbon chain of the alkyl group instantially free from nonaromatic hydrocarbons by means drocarbons with a solvent selected from the class of cyclic .inner amides of gamma-aminolacids, commonly known as gamma-lactams. The gamma-lactams preferred for "purposes of this invention are the alkyl substitutedlactams of gamma-aminobutanoic acid and gamma-amino- I creases. 7 By selective efficiency is meant the ability of the solvent to extract the aromatic hydrocarbons in preference to nonaromatic hydrocarbons and the ability to form discrete phases as a means of obtaining the desired separation.

In practice, the hydrocarbon mixture containing aromatic and nonaromatic hydrocarbons is admixed thoroughly with the selective solvent selected from the aforementioned class of compounds by any suitable means,

such as mechanical agitation or in a countercurrent extraction column, and a small amount of water suflicient to compensate for the decreased selective efliciency is added either to the solventor the solvent-hydrocarbon mixture. Two immiscible phases are formed which are separated. The upper phase or raftinate has an appreciably lower content of aromatic hydrocarbons than the griginal mixture and contains a small amount of selective solvent. The raflinate may be washed with Water to remove the small amount of solvent dissolved therein. The lower extract phase is composed of a solution of aromatic" hydrocarbons in the selective solvent. By the choice of proper solvents inthe class defined, and by regulation of conditions such as temperatures, ratio of selective solvent to the original hydrocarbon mixture, and water content of the selective solvent, varying amounts of the aromataic hydrocarbons originally present can be removed. Thus, it is possible to obtain rafiinates which are substantially free of aromatic'hydrocarbons and ex-v tract phases which contain virtually all of the aromatic hydrocarbons of the original mixture. It is also possible to vary the amount of the aromatic hydrocarbon in the extract phase, depending upon the gamma-lactam used,

water as an aqueous solution immiscible with the aromatic hydrocarbon fraction. Phase separation may be facilitated by dilution with a low-density hydrocarbon or mixture of hydrocarbons. The aromatic fraction, after distilling oii the diluent, may, if desired, be further processed by distillation, but is suitable for many uses without further treatment. Recovery of the selective solvent from the aqueous phase solution is efiected by distillation which gives an aqueous distillate and a residue of solvent.

1 The recovered solvent then may be reused to treat more of the hydrocarbon mixture.

Patented Apr. 19, 1 960 the conditions of the extraction and recovery process,

and have been recycled without evidence of deterioration. The only additional solvent needed is to make up any operating losses. a

The drawing is a diagrammatic representation of a cyclic process using the selective solvents of the present invention in a continuous process for the separation of hydrocarbon mixtures. The arrows in the diagram indicate the direction of flow. The drawing is described with reference to gamma-butyrolactam extraction of light catalytic cycle oil, a refinery product comprising aromatic hydrocarbons and non-aromatic hydrocarbons in the boiling range of 400 to 600 F. The butyrolactam from storage tank 1 is admitted through line 2 to the top of countercurrent extraction column 3. Light catalytic cycle oil from storage tank 4 is fed through line 5 t0 the bottom of the column 3. The ratio of the butyrolactam to hydrocarbon mixturefis maintained at the desired level by controlling the flow rates of the two liquids. In extraction column 3, intimate contact of the butyrolactam with the light catalytic cycle oil is attained and the rafiinate and extract phases are formad and separated. The raflinate rises to the top and passes through line 6 to the bottom of countercurrent extraction column 7. Water is admitted to the top of column 7 through line 8, andany butyrolactam carried over in the ralfinate is removed as a dilute aqueous solution which leaves the bottom of column 7 through line 9. The washed railinate passes through line 10 to raffiuate storage tank 11. If desired, the washed rafiinate may be subjected to further extraction with the gamma-lactams. Also, all or portions of the washed raffinate may be fed back or recycled to the extraction column 3, to obtain further extraction of any aromatic hydrocarbons remaining in the rafiinate.

The extract phase from the bottom of column 3 passes through line 12 to the lower end of countercurrent extraction column 13 where it is contacted and washed with water to separate the butyrolactam from the aromatic hydrocarbon fraction. The latter fraction passes from the top of column 13 through line 14 to the aromatic hydrocarbon storage tank 15. If desired, a relatively low boiling, low-density diluent, such as hexane or gasoline, may be introduced into column 13, along with the extract, to lower the density of the aromatic hydrocarbon fraction and permit easier separation from the aqueous butyrolactam phase. This diluent subsequently may be removed from the higher boiling aromatic hydrocarbons by fractional distillation.

. The aqueous solution of the bulyrolactam obtained from the extract phase is fed from the bottom of column 13 through line 16 to the distillation tower 17. Aqueous butyrolactam from the bottom of column 7 is also fed to tower 17 through line 9. Distillation of the aqueous butyrolactam gives water as the overhead fraction which is condensed in condenser 18 and then used to wash the extract phase by passage through line 19 to the top of column 13; part of this distillate is used to wash.the raffinate by passage through line 20 to the top of column 7. The high-boiling residue from the distillation of the aqueous butyrolactam is substantially pure butyrolactam suitable for reuse. The recovered butyrolactam is removed from the bottom of tower 1'7 and is returned through line 21 to the butyrolactam storage tank 1.

The separation of aromatic hydrocarbons from non- '4 rials in order to decrease viscosities and to facilitate phase disengagement.

The following examples are illustrative of the inventron and are not intended as limitations thereof.

Example I Twenty-five milliliters of light catalytic cycle oll containing about 25 percent, by weight, aromatic hydrocarbons was mixed with 25 milliliters of N-methyl-gammabutyrolactam containing 5 percent, by weight, of water. Upon standing, two immiscible phases separated and the lower-extract phase was drawn off. This lower extract phase was mixed with an equal volume of water to liberate the aromatic hydrocarbons from the solvent. The aromatic hydrocarbon fraction was separated and washed with water to remove residual solvent and dried. This aromatic hydrocarbon fraction amounted to about 28 percent, by weight, of the original light catalytic cycle oil, and was substantially enriched in aromatic hydrocarbon content,-as indicated by the refractive index (11 of 1.5691. 7

At ambient room temperature, the N-ethyl-gammabutyrolactam was ineffective for the separation of an enriched aromatic hydrocarbon fraction from light catalytic cycle oil. It is believed that the ineffectiveness is due to the presence of the ethyl group in the gamma-butyrolactam skeletal nucleus. However, whatever the cause may be, it has been found that the addition of a small amount of water to the alkylated gamma-butyrolactams results in an effective means for extracting aromatic hydrocarbons from a mixture of aromatic and nonaromatic hydrocarbons. This is further illustrated in the following example:

aromatic hydrocarbons by the selective solvents of this Example II Twenty-five milliliters of N-ethyl-gamma-butyrolactam containing 10 percent, by weight, of water was mixed with 25 milliliters of light catalytic cycle oil. On standing, two phases separated, and the lower extract phase was withdrawn. This extract phase was mixed with an equal volume of water to liberate the aromatic hydrocarbon fraction which separated. The aromatic hydrocarbon fraction was washed with water to removeresidual solvent and then dried. This aromatic hydrocarbon fraction amounted to about 20 percent of the original light catalytic cycle oil. It had a refractive index (11 of 1.5762 and represented a productwhich was enriched in aromatic hydrocarbon content, as compared to the original cycle oil.

These examples illustrate that the separation of the extract phase from the rafiinate becomes less discrete and, the selective preference for aromatics over nonaromatics progressively decreases as the number of carbon atoms of the short-chain alkyl groups in the gammalactam nucleus increases. It is preferred that the amount of water used in the extraction step is in the order of about 10 percent, by weight, based on the weight of the gamma-lactam. However, the small amount of water necessary for extraction by the alkylatcd gamma-butyrolactam may be varied, depending upon the number of carbonatoms in the alkyl group. Although this invention is particularly useful for the separation of aromatic hydrocarbons from light catalytic cycle oil, it is contemplated that, the invention may be used in the extraction of other mixtures of aromatic and nonaromatic hy drocarbons. Obviously, there may be many manipulative modifications and variations of the extractive processes in the use of this invention.

What is claimed is: I

1. The process of obtaining an extract rich in aromatic hydrocarbons from a mixture of aromatic and nonaromatic hydrocarbons by means of phase separation comprising extracting said mixture with a selective solvent comprising N-methyl-gamma-butyrolactam and from 5 tor-1Q y eig t of water.

2. The process of obtaining an extract rich in aromatic hydrocarbons from a mixture of aromatic and nonaromatic hydrocarbons by means of phase separation comprising extracting said mixture with a selective solvent comprising N-ethyl-gamma-butyrolactam and from to by weight of water.

3. The process of obtaining an extract rich in aromatic hydrocarbons from light catalytic cycle oil containing hydrocarbons having boiling points in the range of about 400 to about 600 F. comprising extracting said oil with a selective solvent comprising N-methyl-gammabutyrolactam and from 5 to 10% by weight of water.

4. The process or" obtainingan extract rich in aromatic hydrocarbons from light catalytic cycle oil containing hydrocarbons having boiling points in the range of about 400 to about 600 F. comprising extracting said oil with a selective solvent comprising N-ethylgamma-butyrolactam and from 5 to 10% by weight of water.

5. The process of obtaining an extract rich in aromatic hydrocarbons from a mixture of aromatic and nonaromatic hydrocarbons by means of phase separation comprising extraclting said mixture with an N-alkylgamma-butyrolactam wherein said alkyl is a short-chain alkyl group wherein the number of carbon atoms is less than that which renders the lactam in the presence of small amounts of water nonselective for the aromatic hydrocarbons and from 5 to 10% by weight of water.

tural formula R: wherein R is selected from the class consisting of hydrogen and a short-chain alkyl group and R is a shortchain alkyl group, the total number of carbon atoms in both of said alkyl groups being less than that which renders the lactam in the presence of small amounts of water nonselective for the aromatic hydrocarbons.

7. The process of obtaining an extract rich in aromatic hydrocarbons from a mixture of aromatic and nonaromatic hydrocarbons by means of phase separation comprising extracting said mixture with a selective solvent comprising from 5 to 10% by weight of water and a shortchain alkyl substituted, N-ethyl-gamma-butrolactam, the number of carbon atoms in the short-chain alkyl substituent being less than that which renders the lactam in the presence of small amounts of water nonselective for the aromatic hydrocarbons.

8. The process of obtaining an extract rich in aromatic hydrocarbons from a mixture of aromatic and nonarm matic hydrocarbons by means of phase separation, comprising: adding Nethyl-gamma-butyrolactam to said mixture whereby a miscible solution of the butyrolactam and the mixture is obtained; adding from 5 to 10% by weight of water to cause two phases to separate, one of said phases being an aqueous lactam phase containing an enriched extract of aromatic hydrocarbons.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Chemical Abstracts, volume 28, page 7444 (1934), original article in Gazz. Chim. Ital., volume 63, page 495 1933). 

1. THE PROCESS OF OBTAINING AN EXTRACT RICH IN AROMATIC HYDROCARBONS FROM A MIXTURE OF AROMATIC AND NONAROMATIC HYDROCARBONS BY MEANS OF PHASE SEPARATION COMPRISING EXTRACTING SAID MIXTURE WITH A SELECTIVE SOLVENT COMPRISING N-METHYL-GAMMA-BUTYROLACTAM AND FROM 5 TO 10 BY WEIGHT OF WATER. 